This invention relates to valves, more particularly the invention relates to valves with plastic valve bodies and other plastic components which are subject to creep.
In the semiconductor processing industry, highly corrosive or caustic fluids are utilized with temperatures exceeding 150xc2x0 C. Traditional metal valves, fittings, and plumbing are not suitable in such applications. Rather, highly inert materials such as fluoropolymers, for example PFA (perfluoroalkoxy) and PTFE (polytetrafluoroethylene), are utilized. In such applications it is critical to have a very high performance level in valves. Due to the highly caustic ultra-pure chemicals utilized, valve leakage or failure can have economically catastrophic results as well as presenting a hazard to personnel. A problem encountered with plastic in general and plastic valves in particular is that plastic under stress can creep impairing the integrity of the valve. Creep is exacerbated by high temperatures and fluctuating temperatures. Typically, the valve stem, the valve seat, and the valve body are components subject to creep under stress. Such creeping can reduce reliability, lower the life expectancy of such valves, increase maintenance of the valves, and generally increase the costs associated with the valves.
Referring to FIGS. 1 and 2, a prior art manually operated three way valve such as used in the semiconductor processing industry is illustrated and is generally designated with the numeral 10. A valve body 11 has a handle 12 extending therefrom which is rotated to operate the valve. An actuator portion 13 includes the handle, the actuator shaft 14, and a motion translation mechanism 16. The actuator portion is engaged with a valve stem assembly 18 having a first or upper valve member 20 and a second or lower valve member 22 each configured as poppets and each with a diaphragm 24 extending therefrom. The motion translation mechanism 28 may be such as a threaded shaft 32 or cam surfaces 34 for transforming the rotational motion of the handle into linear motion of the valve stem assembly. Both mechanisms are illustrated although only one would generally be used on an individual valve. A first spring 36 is positioned below the lower valve member and provides the seating pressure to seal said lower valve member and the corresponding lower valve seat 40. A supplemental spring 38 may be used. The actuation mechanism operates against the spring force to separate the lower valve member from the valve seat and open the lower valve portion 42.
The upper valve member 20 is moved axially by the motion translation mechanism which may include intermediate connecting members 44. In valves which utilize a threaded actuator shaft, the seating pressure between the valve member and valve seat can be directly dependant upon the torque provided to the handle. A disadvantages of this arrangement is that the seating pressure depends upon the subjective determination of the operator as to when the valve is tight enough. Operators tend to use excessive force closing such valves to be sure they are tight enough. This can result in immediate valve failure or cause excessive creep to the actuator mechanism including the motion translation mechanism, as well as the valve seat and other portions of the valve body. Sufficient creep to be detrimental to the operation of the valve can occur after a limited number of use cycles.
One way of addressing this problem is to provide a stop to limit the rotation of the handle and shaft to take tightening discretion away from the operator. These types of valves also are subject to creep and will typically have an adjusting nut so that the actuator mechanism can be adjusted to compensate for creep. An inherent problem with these valves is knowing when creep has occurred and knowing how much to adjust the adjustment nut. These are often subjective determinations determined by operators and thus are subject to error.
In valves which utilize the cam surfaces, the shaft will typically have a rotational stop and the sealing pressure of the valve member on the valve seat is not dependant upon the torquing of the handle as long as the handle is fully rotated. These cammed translation mechanisms effectively provide a limited rotation, for example, a quarter turn, to effectuate full closure and opening. Plastic valves utilizing the cam surfaces are also subject to creep and where the short one quarter rotation is utilized creep considerations are pronounced. These valves typically will need an adjusting nut such that after extended use the valves can then be adjusted to restore original closure pressures between the upper valve member and valve seat.
Still referring to FIG. 1, plastic valves, particularly those used the semiconductor manufacturing industry, will often have an annular groove or recess 48 at the valve seat. This feature gives the valve seat some flexibility which provides more consistency in seating and sealing, provides lowers manufacturing tolerances for the plastic components, and thus provides lower manufacturing costs. The flexible valve seat also makes the valve seat more susceptible to creep.
A valve is needed that takes the discretion away from the operator in determining how much to torque a plastic valve. A plastic three-way diaphragm valve is needed that does not need periodic adjustment to compensate for creep. A plastic valve is needed that minimizes internal stresses in the valve to minimize the occurrence of creep. A plastic valve is needed that is self-compensating for creep.
A valve made principally of plastic has a creep compensating portion that provides consistent engagement between valve members and their respective valve seats. The features compensate for contraction of internal valve components as well as extension of the valve body. Moreover, the creep compensation portion in embodiments having manual handles, limit the force applied by valve members on the valve seats. Valves according to the invention are particularly suitable for applications in the semiconductor industry.
One embodiment of the invention is a three-way diaphragm valve configuration having a first flow duct, a second flow duct, and a common flow duct. Valve portions control the flow between the first flow duct and the common flow duct as well as between the second flow duct and the common flow duct. An actuation portion operatively connected to a creep compensating portion to control the closing force provided by a first valve member on a first valve seat and a second valve member on a second valve seat. The creep compensating portion comprises a pair of captured spring mechanisms. The captured spring mechanisms self compensate for any creep of the valve components while maintaining substantially constant closure force.
In one preferred embodiment of the invention, the actuator portion includes an actuator connecting portion that moves axially up and down by rotation of a handle. This causes the valve stem assembly to move axially and the valve portions to open and close. The actuator connecting portion extends through the hollow stem and is directly engaged with the valve member of the lower valve portion and is axially slidable within the first valve member.
In said preferred embodiment, the lower spring provides upward bias to the valve stem assembly and specifically provides upward force to close the lower valve portion when the actuator connecting portion is not holding the lower valve member open. When the actuator assembly moves downwardly by rotation of the handle, the actuator shaft causes the lower valve member to be separated from the lower valve seat and correspondingly causes the first spring to be compressed by the actuator shaft. Additionally, the downward movement of the actuator assembly pushes down on the upper valve member of the upper valve portion through a creep compensating mechanism to seat the upper valve member on the upper valve seat. The creep compensating mechanism is comprised of a captured preloaded spring mechanism. The mechanism has an extended position and by providing sufficient axial compressive force may be compressed to a contracted and compressed position. The actuator mechanism is configured such that the upper valve member seats before the handle is rotated through its complete range of motion. As the handle is further rotated, the upper valve member remains seated and further downward movement of the actuator assembly compresses the trapped preloaded spring mechanism. This additional available movement of the actuator assembly then does not require a corresponding motion of the upper valve member. Thus if the valve stem compresses, that is shortens, due to creep of the plastic valve stem, the first valve member will seat slightly later that with an uncompressed valve stem and the trapped spring mechanism will still compress but will compress later in the rotational movement of the handle and will compress slightly less. The downward force of the valve member on the valve seat will be substantially the same as in the case of the uncompressed valve stem. Thus the trapped spring mechanism effectively and automatically compensates for the compressive creep in the valve stem assembly. Expansive creep in the valve body members is compensated for in a similar fashion.
A feature and advantage of particular embodiments of the invention is that valves made in accordance therewith are subjected to minimal and controlled internal stresses thereby minimizing the occurrence of creep.
A feature and advantage of particular embodiments of the invention is that creep is automatically compensated for by the valve without the need for adjustment.
A feature and advantage of certain embodiments of the invention is that no adjustment nut is needed.
A feature and advantage provided by particular embodiments of the invention is a plastic valve with a greater degree of reliability and longer life expectancy.
A feature and advantage of particular embodiments of the invention is that a quarter turn valve three way valve is possible without an adjustment nut and that has extended life expectancy and improved reliability compared to known quarter turn three-way valves.
A further significant feature and advantage of particular embodiments of the invention is that the closure force of each valve member is provided by the deflection of a separate spring. Moreover, the springs do not operate against each other to put additional stress on internal valve components. This minimizes the occurrence of creep.
Various embodiments of the invention are illustrated and described below. Note that the words xe2x80x9cconnectxe2x80x9d, xe2x80x9cconnectionxe2x80x9d, and xe2x80x9cconnectingxe2x80x9d when used herein do not require direct physical contact between the involved component, that is, intermediate components may be present. Where reference is made to a plastic valve, this does not require all components of the valve be made of plastic, only that the valve is principally constructed of plastic. Moreover, xe2x80x9cspringxe2x80x9d when used herein may comprise a single or multiple springs. When directions are indicated herein, such as xe2x80x9cupxe2x80x9d, xe2x80x9cdownxe2x80x9d, xe2x80x9cupwardlyxe2x80x9d, and xe2x80x9cdownwardlyxe2x80x9d, these are to be construed only as references relative positions of the valve elements and components and are not to be construed as requiring the valve or components to be placed in a specific orientation in the environment in which the valve is utilized.